Dreamlogs, writing + music and thoughts

So I’m currently working on another short original thing like the things I did for 750 Words, but I keep stalling and screeching to a halt. I feel like a terrible writer. I know beginners aren’t able to write like writers do, but it feels like it definitely isn’t normal to be so bad at writing fluidly. I keep grinding to a halt while I think about what I do next. Am I supposed to brainstorm and get a rough outline of the points I’m supposed to be hitting beforehand? I’ve written freely once. Only once have I been able to write without any idea as to where I’m going. Now I can’t do that, and I’m never going to be even remotely decent at writing if I can’t even get the proper ways and techniques for writing down.